The article is not exceptionally clear. Did they make Mach 6, and lose the fin during acceleration, or were they in the process of boosting to Mach 6. They menion later in the article that the Scramjet itself was never activated?

Interestingly enough the story was pretty big in the German media. I found it in a couple of papers/magazines.
The fin problem apparently started 16 seconds after the launch from the B52. The article mentions that control was lost another 15s after that when discarding the rocket engine.

A superfast unmanned military plane traveled at 20 times the speed of sound and managed to control itself for three minutes before crashing into the Pacific Ocean in a recent test, military officials said.